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Misha Brukman6c2522a2008-12-10 23:07:02 +0000[diff] [blame]6 <title>LLVM Coding Standards</title>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]7</head>
8<body>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]9
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]10<div class="doc_title">
Misha Brukman6c2522a2008-12-10 23:07:02 +0000[diff] [blame]11 LLVM Coding Standards
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]12</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]13
14<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner85014f42001-07-23 20:40:41 +0000[diff] [blame]16 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]17 <ol>
18 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]19 <ol>
20 <li><a href="#scf_commenting">Commenting</a></li>
21 <li><a href="#scf_commentformat">Comment Formatting</a></li>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]22 <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]23 <li><a href="#scf_codewidth">Source Code Width</a></li>
24 <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
25 <li><a href="#scf_indentation">Indent Code Consistently</a></li>
26 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]27 <li><a href="#compilerissues">Compiler Issues</a>
28 <ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]29 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
30 Errors</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]31 <li><a href="#ci_portable_code">Write Portable Code</a></li>
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]32 <li><a href="#ci_class_struct">Use of class/struct Keywords</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]33 </ol></li>
34 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]35 <li><a href="#styleissues">Style Issues</a>
36 <ol>
37 <li><a href="#macro">The High Level Issues</a>
38 <ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]39 <li><a href="#hl_module">A Public Header File <b>is</b> a
40 Module</a></li>
41 <li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
42 <li><a href="#hl_privateheaders">Keep "internal" Headers
43 Private</a></li>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]44 <li><a href="#hl_earlyexit">Use Early Exits and 'continue' to Simplify
45 Code</a></li>
46 <li><a href="#hl_predicateloops">Turn Predicate Loops into Predicate
47 Functions</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]48 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]49 <li><a href="#micro">The Low Level Issues</a>
50 <ol>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]51 <li><a href="#ll_assert">Assert Liberally</a></li>
52 <li><a href="#ll_ns_std">Do not use 'using namespace std'</a></li>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]53 <li><a href="#ll_virtual_anch">Provide a virtual method anchor for
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]54 classes in headers</a></li>
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]55 <li><a href="#ll_end">Don't evaluate end() every time through a
56 loop</a></li>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]57 <li><a href="#ll_iostream"><tt>#include &lt;iostream&gt;</tt> is
58 <em>forbidden</em></a></li>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]59 <li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]60 </ol></li>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]61
62 <li><a href="#nano">Microscopic Details</a>
63 <ol>
64 <li><a href="#micro_spaceparen">Spaces Before Parentheses</a></li>
65 <li><a href="#micro_preincrement">Prefer Preincrement</a></li>
66 <li><a href="#micro_namespaceindent">Namespace Indentation</a></li>
67 <li><a href="#micro_anonns">Anonymous Namespaces</a></li>
68 </ol></li>
69
70
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]71 </ol></li>
72 <li><a href="#seealso">See Also</a></li>
73</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]74
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]75<div class="doc_author">
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]76 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
77 <a href="mailto:void@nondot.org">Bill Wendling</a></p>
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]78</div>
79
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]80
81<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]82<div class="doc_section">
83 <a name="introduction">Introduction</a>
84</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]85<!-- *********************************************************************** -->
86
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]87<div class="doc_text">
88
89<p>This document attempts to describe a few coding standards that are being used
90in the LLVM source tree. Although no coding standards should be regarded as
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]91absolute requirements to be followed in all instances, coding standards can be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]92useful.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]93
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]94<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]95issues such as brace placement and space usage. For issues like this, follow
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]96the golden rule:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]97
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]98<blockquote>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]99
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]100<p><b><a name="goldenrule">If you are adding a significant body of source to a
101project, feel free to use whatever style you are most comfortable with. If you
102are extending, enhancing, or bug fixing already implemented code, use the style
103that is already being used so that the source is uniform and easy to
104follow.</a></b></p>
105
106</blockquote>
107
108<p>The ultimate goal of these guidelines is the increase readability and
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]109maintainability of our common source base. If you have suggestions for topics to
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]110be included, please mail them to <a
111href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]112
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]113</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]114
115<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]116<div class="doc_section">
117 <a name="mechanicalissues">Mechanical Source Issues</a>
118</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]119<!-- *********************************************************************** -->
120
121<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]122<div class="doc_subsection">
123 <a name="sourceformating">Source Code Formatting</a>
124</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]125
126<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]127<div class="doc_subsubsection">
128 <a name="scf_commenting">Commenting</a>
129</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]130
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]131<div class="doc_text">
132
133<p>Comments are one critical part of readability and maintainability. Everyone
Chris Lattnerbbe228b2009-07-12 00:10:24 +0000[diff] [blame]134knows they should comment, so should you. When writing comments, write them as
135English prose, which means they should use proper capitalization, punctuation,
136etc. Although we all should probably
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]137comment our code more than we do, there are a few very critical places that
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]138documentation is very useful:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]139
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]140<b>File Headers</b>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]141
Reid Spencerc7f87f22007-07-09 08:04:31 +0000[diff] [blame]142<p>Every source file should have a header on it that describes the basic
143purpose of the file. If a file does not have a header, it should not be
144checked into Subversion. Most source trees will probably have a standard
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]145file header format. The standard format for the LLVM source tree looks like
146this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]147
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]148<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]149<pre>
Chris Lattnere6f4e072003-10-13 14:58:11 +0000[diff] [blame]150//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Misha Brukman02805a62009-01-02 16:58:42 +0000[diff] [blame]151//
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]152// The LLVM Compiler Infrastructure
153//
Chris Lattnerebf56662007-12-29 19:56:08 +0000[diff] [blame]154// This file is distributed under the University of Illinois Open Source
155// License. See LICENSE.TXT for details.
Misha Brukman02805a62009-01-02 16:58:42 +0000[diff] [blame]156//
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]157//===----------------------------------------------------------------------===//
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]158//
159// This file contains the declaration of the Instruction class, which is the
160// base class for all of the VM instructions.
161//
162//===----------------------------------------------------------------------===//
163</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]164</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]165
Chris Lattnerebf56662007-12-29 19:56:08 +0000[diff] [blame]166<p>A few things to note about this particular format: The "<tt>-*- C++
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]167-*-</tt>" string on the first line is there to tell Emacs that the source file
Misha Brukman0d640e82004-07-28 22:37:57 +0000[diff] [blame]168is a C++ file, not a C file (Emacs assumes .h files are C files by default).
169Note that this tag is not necessary in .cpp files. The name of the file is also
170on the first line, along with a very short description of the purpose of the
171file. This is important when printing out code and flipping though lots of
172pages.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]173
Chris Lattnerebf56662007-12-29 19:56:08 +0000[diff] [blame]174<p>The next section in the file is a concise note that defines the license
175that the file is released under. This makes it perfectly clear what terms the
176source code can be distributed under and should not be modified in any way.</p>
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]177
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]178<p>The main body of the description does not have to be very long in most cases.
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]179Here it's only two lines. If an algorithm is being implemented or something
180tricky is going on, a reference to the paper where it is published should be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]181included, as well as any notes or "gotchas" in the code to watch out for.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]182
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]183<b>Class overviews</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]184
Jim Laskey88b5e792006-07-31 20:18:49 +0000[diff] [blame]185<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]186a class definition should have a comment block that explains what the class is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]187used for... if it's not obvious. If it's so completely obvious your grandma
188could figure it out, it's probably safe to leave it out. Naming classes
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]189something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]190
191
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]192<b>Method information</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]193
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]194<p>Methods defined in a class (as well as any global functions) should also be
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]195documented properly. A quick note about what it does any a description of the
196borderline behaviour is all that is necessary here (unless something
197particularly tricky or insideous is going on). The hope is that people can
198figure out how to use your interfaces without reading the code itself... that is
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]199the goal metric.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]200
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]201<p>Good things to talk about here are what happens when something unexpected
202happens: does the method return null? Abort? Format your hard disk?</p>
203
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]204</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]205
206<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]207<div class="doc_subsubsection">
208 <a name="scf_commentformat">Comment Formatting</a>
209</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]210
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]211<div class="doc_text">
212
213<p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]214require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]215when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]216
217<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]218 <li>When writing a C code: Obviously if you are writing C code, use C style
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]219 comments.</li>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]220 <li>When writing a header file that may be <tt>#include</tt>d by a C source
221 file.</li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]222 <li>When writing a source file that is used by a tool that only accepts C
223 style comments.</li>
224</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]225
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]226<p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
227These nest properly and are better behaved in general than C style comments.</p>
228
229</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]230
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]231<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]232<div class="doc_subsubsection">
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]233 <a name="scf_includes"><tt>#include</tt> Style</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]234</div>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]235
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]236<div class="doc_text">
237
238<p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]239include guards if working on a header file), the <a
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]240href="#hl_dontinclude">minimal</a> list of <tt>#include</tt>s required by the
241file should be listed. We prefer these <tt>#include</tt>s to be listed in this
242order:</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]243
244<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]245 <li><a href="#mmheader">Main Module header</a></li>
246 <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]247 <li><tt>llvm/*</tt></li>
248 <li><tt>llvm/Analysis/*</tt></li>
249 <li><tt>llvm/Assembly/*</tt></li>
250 <li><tt>llvm/Bytecode/*</tt></li>
251 <li><tt>llvm/CodeGen/*</tt></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]252 <li>...</li>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]253 <li><tt>Support/*</tt></li>
254 <li><tt>Config/*</tt></li>
255 <li>System <tt>#includes</tt></li>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]256</ol>
257
Nick Lewycky35847802008-11-29 20:13:25 +0000[diff] [blame]258<p>... and each category should be sorted by name.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]259
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]260<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]261which implement an interface defined by a .h file. This <tt>#include</tt>
262should always be included <b>first</b> regardless of where it lives on the file
263system. By including a header file first in the .cpp files that implement the
264interfaces, we ensure that the header does not have any hidden dependencies
265which are not explicitly #included in the header, but should be. It is also a
266form of documentation in the .cpp file to indicate where the interfaces it
267implements are defined.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]268
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]269</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]270
271<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]272<div class="doc_subsubsection">
273 <a name="scf_codewidth">Source Code Width</a>
274</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]275
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]276<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]277
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]278<p>Write your code to fit within 80 columns of text. This helps those of us who
279like to print out code and look at your code in an xterm without resizing
280it.</p>
281
Chris Lattnerfc12d2e2008-07-08 05:12:37 +0000[diff] [blame]282<p>The longer answer is that there must be some limit to the width of the code
283in order to reasonably allow developers to have multiple files side-by-side in
284windows on a modest display. If you are going to pick a width limit, it is
285somewhat arbitrary but you might as well pick something standard. Going with
28690 columns (for example) instead of 80 columns wouldn't add any significant
287value and would be detrimental to printing out code. Also many other projects
288have standardized on 80 columns, so some people have already configured their
289editors for it (vs something else, like 90 columns).</p>
290
291<p>This is one of many contentious issues in coding standards, but is not up
292for debate.</p>
293
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]294</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]295
296<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]297<div class="doc_subsubsection">
298 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
299</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]300
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]301<div class="doc_text">
302
303<p>In all cases, prefer spaces to tabs in source files. People have different
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]304prefered indentation levels, and different styles of indentation that they
305like... this is fine. What isn't is that different editors/viewers expand tabs
306out to different tab stops. This can cause your code to look completely
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]307unreadable, and it is not worth dealing with.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]308
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]309<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]310style of existing code if your are modifying and extending it. If you like four
311spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
312with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]313makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]314
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]315</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]316
317<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]318<div class="doc_subsubsection">
319 <a name="scf_indentation">Indent Code Consistently</a>
320</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]321
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]322<div class="doc_text">
323
324<p>Okay, your first year of programming you were told that indentation is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]325important. If you didn't believe and internalize this then, now is the time.
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]326Just do it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]327
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]328</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]329
330
331<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]332<div class="doc_subsection">
333 <a name="compilerissues">Compiler Issues</a>
334</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]335
336
337<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]338<div class="doc_subsubsection">
339 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
340</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]341
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]342<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]343
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]344<p>If your code has compiler warnings in it, something is wrong: you aren't
345casting values correctly, your have "questionable" constructs in your code, or
346you are doing something legitimately wrong. Compiler warnings can cover up
347legitimate errors in output and make dealing with a translation unit
348difficult.</p>
349
350<p>It is not possible to prevent all warnings from all compilers, nor is it
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]351desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
352a good thorough set of warnings, and stick to them. At least in the case of
353<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
354syntax of the code slightly. For example, an warning that annoys me occurs when
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]355I write code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]356
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]357<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]358<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]359if (V = getValue()) {
360 ...
361}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]362</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]363</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]364
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]365<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
366operator, and that I probably mistyped it. In most cases, I haven't, and I
367really don't want the spurious errors. To fix this particular problem, I
368rewrite the code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]369
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]370<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]371<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]372if ((V = getValue())) {
373 ...
374}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]375</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]376</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]377
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]378<p>...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
379be fixed by massaging the code appropriately.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]380
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]381<p>These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall
382-Winline -W -Wwrite-strings -Wno-unused</tt></p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]383
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]384</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]385
386<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]387<div class="doc_subsubsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]388 <a name="ci_portable_code">Write Portable Code</a>
389</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]390
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]391<div class="doc_text">
392
393<p>In almost all cases, it is possible and within reason to write completely
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]394portable code. If there are cases where it isn't possible to write portable
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]395code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]396
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]397<p>In practice, this means that you shouldn't assume much about the host
398compiler, including its support for "high tech" features like partial
Chris Lattner30bc9722009-03-23 04:52:53 +0000[diff] [blame]399specialization of templates. If these features are used, they should only be
400an implementation detail of a library which has a simple exposed API.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]401
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]402</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]403
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]404<!-- _______________________________________________________________________ -->
405<div class="doc_subsubsection">
406<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
407</div>
408<div class="doc_text">
Misha Brukmanf2499132004-10-26 15:45:13 +0000[diff] [blame]409
410<p>In C++, the <tt>class</tt> and <tt>struct</tt> keywords can be used almost
411interchangeably. The only difference is when they are used to declare a class:
412<tt>class</tt> makes all members private by default while <tt>struct</tt> makes
413all members public by default.</p>
414
415<p>Unfortunately, not all compilers follow the rules and some will generate
416different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used to
417declare the symbol. This can lead to problems at link time.</p>
418
419<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
420<b>all</b> members are public, in which case <tt>struct</tt> is allowed.</p>
421
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]422</div>
423
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]424<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]425<div class="doc_section">
426 <a name="styleissues">Style Issues</a>
427</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]428<!-- *********************************************************************** -->
429
430
431<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]432<div class="doc_subsection">
433 <a name="macro">The High Level Issues</a>
434</div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]435<!-- ======================================================================= -->
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]436
437
438<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]439<div class="doc_subsubsection">
440 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
441</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]442
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]443<div class="doc_text">
444
445<p>C++ doesn't do too well in the modularity department. There is no real
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]446encapsulation or data hiding (unless you use expensive protocol classes), but it
447is what we have to work with. When you write a public header file (in the LLVM
448source tree, they live in the top level "include" directory), you are defining a
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]449module of functionality.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]450
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]451<p>Ideally, modules should be completely independent of each other, and their
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]452header files should only include the absolute minimum number of headers
453possible. A module is not just a class, a function, or a namespace: <a
454href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection
455of these</a> that defines an interface. This interface may be several
456functions, classes or data structures, but the important issue is how they work
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]457together.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]458
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]459<p>In general, a module should be implemented with one or more <tt>.cpp</tt>
460files. Each of these <tt>.cpp</tt> files should include the header that defines
461their interface first. This ensure that all of the dependences of the module
462header have been properly added to the module header itself, and are not
463implicit. System headers should be included after user headers for a
464translation unit.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]465
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]466</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]467
468<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]469<div class="doc_subsubsection">
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]470 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]471</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]472
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]473<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]474
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]475<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
476have to, especially in header files.</p>
477
478<p>But wait, sometimes you need to have the definition of a class to use it, or
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]479to inherit from it. In these cases go ahead and <tt>#include</tt> that header
480file. Be aware however that there are many cases where you don't need to have
481the full definition of a class. If you are using a pointer or reference to a
482class, you don't need the header file. If you are simply returning a class
483instance from a prototyped function or method, you don't need it. In fact, for
484most cases, you simply don't need the definition of a class... and not
485<tt>#include</tt>'ing speeds up compilation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]486
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]487<p>It is easy to try to go too overboard on this recommendation, however. You
Chris Lattner756f83f2007-02-10 18:35:31 +0000[diff] [blame]488<b>must</b> include all of the header files that you are using -- you can
489include them either directly
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]490or indirectly (through another header file). To make sure that you don't
491accidently forget to include a header file in your module header, make sure to
492include your module header <b>first</b> in the implementation file (as mentioned
493above). This way there won't be any hidden dependencies that you'll find out
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]494about later...</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]495
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]496</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]497
498<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]499<div class="doc_subsubsection">
500 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
501</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]502
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]503<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]504
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]505<p>Many modules have a complex implementation that causes them to use more than
506one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
507internal communication interface (helper classes, extra functions, etc) in the
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]508public module header file. Don't do this.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]509
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]510<p>If you really need to do something like this, put a private header file in
511the same directory as the source files, and include it locally. This ensures
512that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]513
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]514<p>Note however, that it's okay to put extra implementation methods a public
515class itself... just make them private (or protected), and all is well.</p>
516
517</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]518
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]519<!-- _______________________________________________________________________ -->
520<div class="doc_subsubsection">
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]521 <a name="hl_earlyexit">Use Early Exits and 'continue' to Simplify Code</a>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]522</div>
523
524<div class="doc_text">
525
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]526<p>When reading code, keep in mind how much state and how many previous
527decisions have to be remembered by the reader to understand a block of code.
528Aim to reduce indentation where possible when it doesn't make it more difficult
529to understand the code. One great way to do this is by making use of early
530exits and the 'continue' keyword in long loops. As an example of using an early
531exit from a function, consider this "bad" code:</p>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]532
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]533<div class="doc_code">
534<pre>
535Value *DoSomething(Instruction *I) {
536 if (!isa&lt;TerminatorInst&gt;(I) &amp;&amp;
537 I-&gt;hasOneUse() &amp;&amp; SomeOtherThing(I)) {
538 ... some long code ....
539 }
540
541 return 0;
542}
543</pre>
544</div>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]545
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]546<p>This code has several problems if the body of the 'if' is large. When you're
547looking at the top of the function, it isn't immediately clear that this
548<em>only</em> does interesting things with non-terminator instructions, and only
549applies to things with the other predicates. Second, it is relatively difficult
550to describe (in comments) why these predicates are important because the if
551statement makes it difficult to lay out the comments. Third, when you're deep
552within the body of the code, it is indented an extra level. Finally, when
553reading the top of the function, it isn't clear what the result is if the
554predicate isn't true, you have to read to the end of the function to know that
555it returns null.</p>
Matthijs Kooijmanca4ffaa2008-07-30 12:14:10 +0000[diff] [blame]556
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]557<p>It is much preferred to format the code like this:</p>
558
559<div class="doc_code">
560<pre>
561Value *DoSomething(Instruction *I) {
562 // Terminators never need 'something' done to them because, ...
563 if (isa&lt;TerminatorInst&gt;(I))
564 return 0;
565
566 // We conservatively avoid transforming instructions with multiple uses
567 // because goats like cheese.
568 if (!I-&gt;hasOneUse())
569 return 0;
570
571 // This is really just here for example.
572 if (!SomeOtherThing(I))
573 return 0;
574
575 ... some long code ....
576}
577</pre>
578</div>
579
580<p>This fixes these problems. A similar problem frequently happens in for
581loops. A silly example is something like this:</p>
582
583<div class="doc_code">
584<pre>
585 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
586 if (BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II)) {
587 Value *LHS = BO-&gt;getOperand(0);
588 Value *RHS = BO-&gt;getOperand(1);
589 if (LHS != RHS) {
590 ...
591 }
592 }
593 }
594</pre>
595</div>
596
597<p>When you have very very small loops, this sort of structure is fine, but if
598it exceeds more than 10-15 lines, it becomes difficult for people to read and
599understand at a glance.
600The problem with this sort of code is that it gets very nested very quickly,
601meaning that the reader of the code has to keep a lot of context in their brain
602to remember what is going immediately on in the loop, because they don't know
603if/when the if conditions will have elses etc. It is strongly preferred to
604structure the loop like this:</p>
605
606<div class="doc_code">
607<pre>
608 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
609 BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II);
610 if (!BO) continue;
611
612 Value *LHS = BO-&gt;getOperand(0);
613 Value *RHS = BO-&gt;getOperand(1);
614 if (LHS == RHS) continue;
615 }
616</pre>
617</div>
618
619<p>This has all the benefits of using early exits from functions: it reduces
620nesting of the loop, it makes it easier to describe why the conditions are true,
621and it makes it obvious to the reader that there is no "else" coming up that
622they have to push context into their brain for. If a loop is large, this can
623be a big understandability win.</p>
624
625</div>
626
627
628<!-- _______________________________________________________________________ -->
629<div class="doc_subsubsection">
630 <a name="hl_predicateloops">Turn Predicate Loops into Predicate Functions</a>
631</div>
632
633<div class="doc_text">
634
635<p>It is very common to write inline functions that just compute a boolean
636 value. There are a number of ways that people commonly write these, but an
637 example of this sort of thing is:</p>
638
639<div class="doc_code">
640<pre>
641 <b>bool FoundFoo = false;</b>
642 for (unsigned i = 0, e = BarList.size(); i != e; ++i)
643 if (BarList[i]-&gt;isFoo()) {
644 <b>FoundFoo = true;</b>
645 break;
646 }
647
648 <b>if (FoundFoo) {</b>
649 ...
650 }
651</pre>
652</div>
653
654<p>This sort of code is awkward to write, and is almost always a bad sign.
655Instead of this sort of loop, we strongly prefer to use a predicate function
656(which may be <a href="#micro_anonns">static</a>) that uses
657<a href="#hl_earlyexit">early exits</a> to compute the predicate. Code like
658this would be preferred:
659</p>
660
661
662<div class="doc_code">
663<pre>
664/// ListContainsFoo - Return true if the specified list has an element that is
665/// a foo.
666static bool ListContainsFoo(const std::vector&lt;Bar*&gt; &amp;List) {
667 for (unsigned i = 0, e = List.size(); i != e; ++i)
668 if (List[i]-&gt;isFoo())
669 return true;
670 return false;
671}
672...
673
674 <b>if (ListContainsFoo(BarList)) {</b>
675 ...
676 }
677</pre>
678</div>
679
680<p>There are many reasons for doing this: it reduces indentation and factors out
681code which can often be shared by other code that checks for the same predicate.
682More importantly, it <em>forces you to pick a name</em> for the function, and
683forces you to write a comment for it. In this silly example, this doesn't add
684much value. However, if the condition is complex, this can make it a lot easier
685for the reader to understand the code that queries for this predicate. Instead
686of being faced with the in-line details of we check to see if the BarList
687contains a foo, we can trust the function name and continue reading with better
688locality.</p>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]689
690</div>
691
692
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]693<!-- ======================================================================= -->
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]694<div class="doc_subsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]695 <a name="micro">The Low Level Issues</a>
696</div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]697<!-- ======================================================================= -->
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]698
699
700<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]701<div class="doc_subsubsection">
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]702 <a name="ll_assert">Assert Liberally</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]703</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]704
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]705<div class="doc_text">
706
707<p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]708preconditions and assumptions, you never know when a bug (not neccesarily even
709yours) might be caught early by an assertion, which reduces debugging time
710dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
711included by the header files you are using, so it doesn't cost anything to use
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]712it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]713
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]714<p>To further assist with debugging, make sure to put some kind of error message
715in the assertion statement (which is printed if the assertion is tripped). This
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]716helps the poor debugging make sense of why an assertion is being made and
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]717enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]718
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]719<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]720<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]721inline Value *getOperand(unsigned i) {
722 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
723 return Operands[i];
724}
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]725</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]726</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]727
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]728<p>Here are some examples:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]729
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]730<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]731<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]732assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]733
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]734assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]735
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]736assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]737
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]738assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]739
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]740assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]741</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]742</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]743
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]744<p>You get the idea...</p>
745
Nick Lewyckyfb75d422008-05-31 23:54:55 +0000[diff] [blame]746<p>Please be aware when adding assert statements that not all compilers are aware of
747the semantics of the assert. In some places, asserts are used to indicate a piece of
748code that should not be reached. These are typically of the form:</p>
749
750<div class="doc_code">
751<pre>
Dan Gohman8ef44982008-11-24 17:18:39 +0000[diff] [blame]752assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyfb75d422008-05-31 23:54:55 +0000[diff] [blame]753</pre>
754</div>
755
756<p>When used in a function that returns a value, they should be followed with a return
757statement and a comment indicating that this line is never reached. This will prevent
758a compiler which is unable to deduce that the assert statement never returns from
759generating a warning.</p>
760
761<div class="doc_code">
762<pre>
Dan Gohman8ef44982008-11-24 17:18:39 +0000[diff] [blame]763assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyfb75d422008-05-31 23:54:55 +0000[diff] [blame]764// Not reached
765return 0;
766</pre>
767</div>
768
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]769</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]770
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]771<!-- _______________________________________________________________________ -->
772<div class="doc_subsubsection">
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]773 <a name="ll_ns_std">Do not use '<tt>using namespace std</tt>'</a>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]774</div>
775
776<div class="doc_text">
777<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]778namespace with an "<tt>std::</tt>" prefix, rather than rely on
779"<tt>using namespace std;</tt>".</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]780
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]781<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
Misha Brukman586a15c2008-12-11 19:37:04 +0000[diff] [blame]782the namespace of any source file that <tt>#include</tt>s the header. This is
783clearly a bad thing.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]784
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]785<p>In implementation files (e.g. .cpp files), the rule is more of a stylistic
786rule, but is still important. Basically, using explicit namespace prefixes
787makes the code <b>clearer</b>, because it is immediately obvious what facilities
788are being used and where they are coming from, and <b>more portable</b>, because
789namespace clashes cannot occur between LLVM code and other namespaces. The
790portability rule is important because different standard library implementations
791expose different symbols (potentially ones they shouldn't), and future revisions
792to the C++ standard will add more symbols to the <tt>std</tt> namespace. As
793such, we never use '<tt>using namespace std;</tt>' in LLVM.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]794
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]795<p>The exception to the general rule (i.e. it's not an exception for
796the <tt>std</tt> namespace) is for implementation files. For example, all of
797the code in the LLVM project implements code that lives in the 'llvm' namespace.
798As such, it is ok, and actually clearer, for the .cpp files to have a '<tt>using
799namespace llvm</tt>' directive at their top, after the <tt>#include</tt>s. The
800general form of this rule is that any .cpp file that implements code in any
801namespace may use that namespace (and its parents'), but should not use any
802others.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]803
804</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]805
806<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]807<div class="doc_subsubsection">
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]808 <a name="ll_virtual_anch">Provide a virtual method anchor for classes
809 in headers</a>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]810</div>
811
812<div class="doc_text">
813
814<p>If a class is defined in a header file and has a v-table (either it has
815virtual methods or it derives from classes with virtual methods), it must
816always have at least one out-of-line virtual method in the class. Without
Misha Brukman586a15c2008-12-11 19:37:04 +0000[diff] [blame]817this, the compiler will copy the vtable and RTTI into every <tt>.o</tt> file
818that <tt>#include</tt>s the header, bloating <tt>.o</tt> file sizes and
819increasing link times.</p>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]820
821</div>
822
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]823<!-- _______________________________________________________________________ -->
824<div class="doc_subsubsection">
825 <a name="ll_end">Don't evaluate end() every time through a loop</a>
826</div>
827
828<div class="doc_text">
829
830<p>Because C++ doesn't have a standard "foreach" loop (though it can be emulated
831with macros and may be coming in C++'0x) we end up writing a lot of loops that
832manually iterate from begin to end on a variety of containers or through other
833data structures. One common mistake is to write a loop in this style:</p>
834
835<div class="doc_code">
836<pre>
837 BasicBlock *BB = ...
838 for (BasicBlock::iterator I = BB->begin(); I != <b>BB->end()</b>; ++I)
839 ... use I ...
840</pre>
841</div>
842
843<p>The problem with this construct is that it evaluates "<tt>BB->end()</tt>"
844every time through the loop. Instead of writing the loop like this, we strongly
845prefer loops to be written so that they evaluate it once before the loop starts.
846A convenient way to do this is like so:</p>
847
848<div class="doc_code">
849<pre>
850 BasicBlock *BB = ...
851 for (BasicBlock::iterator I = BB->begin(), E = <b>BB->end()</b>; I != E; ++I)
852 ... use I ...
853</pre>
854</div>
855
856<p>The observant may quickly point out that these two loops may have different
857semantics: if the container (a basic block in this case) is being mutated, then
858"<tt>BB->end()</tt>" may change its value every time through the loop and the
859second loop may not in fact be correct. If you actually do depend on this
Chris Lattner6ad089c2009-06-30 06:20:03 +0000[diff] [blame]860behavior, please write the loop in the first form and add a comment indicating
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]861that you did it intentionally.</p>
862
863<p>Why do we prefer the second form (when correct)? Writing the loop in the
864first form has two problems: First it may be less efficient than evaluating it
865at the start of the loop. In this case, the cost is probably minor: a few extra
866loads every time through the loop. However, if the base expression is more
867complex, then the cost can rise quickly. I've seen loops where the end
868expression was actually something like: "<tt>SomeMap[x]->end()</tt>" and map
Chris Lattner67f2a4ac2009-06-30 06:27:54 +0000[diff] [blame]869lookups really aren't cheap. By writing it in the second form consistently, you
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]870eliminate the issue entirely and don't even have to think about it.</p>
871
Chris Lattner6ad089c2009-06-30 06:20:03 +0000[diff] [blame]872<p>The second (even bigger) issue is that writing the loop in the first form
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]873hints to the reader that the loop is mutating the container (a fact that a
874comment would handily confirm!). If you write the loop in the second form, it
875is immediately obvious without even looking at the body of the loop that the
876container isn't being modified, which makes it easier to read the code and
877understand what it does.</p>
878
879<p>While the second form of the loop is a few extra keystrokes, we do strongly
880prefer it.</p>
881
882</div>
883
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]884<!-- _______________________________________________________________________ -->
885<div class="doc_subsubsection">
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]886 <a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is forbidden</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]887</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]888
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]889<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]890
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]891<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
892hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
893support clients using LLVM libraries as part of larger systems. In particular,
894we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
895the static c'tors are run whenever an application start up that uses the dynamic
896library. There are two problems with this:</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]897
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]898<ol>
899 <li>The time to run the static c'tors impacts startup time of
900 applications&mdash;a critical time for GUI apps.</li>
901 <li>The static c'tors cause the app to pull many extra pages of memory off the
902 disk: both the code for the static c'tors in each <tt>.o</tt> file and the
903 small amount of data that gets touched. In addition, touched/dirty pages
904 put more pressure on the VM system on low-memory machines.</li>
905</ol>
906
907<p>Note that using the other stream headers (<tt>&lt;sstream&gt;</tt> for
908example) is allowed normally, it is just <tt>&lt;iostream&gt;</tt> that is
909causing problems.</p>
910
911<p>The preferred replacement for stream functionality is the
912<tt>llvm::raw_ostream</tt> class (for writing to output streams of various
913sorts) and the <tt>llvm::MemoryBuffer</tt> API (for reading in files).</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]914
915</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]916
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]917
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]918<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]919<div class="doc_subsubsection">
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]920 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]921</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]922
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]923<div class="doc_text">
924
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]925<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
926to the output stream specified. In addition to doing this, however, it also
927flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]928
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]929<div class="doc_code">
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]930<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]931std::cout &lt;&lt; std::endl;
932std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]933</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]934</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]935
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]936<p>Most of the time, you probably have no reason to flush the output stream, so
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]937it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]938
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]939</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]940
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]941
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame^]942<!-- ======================================================================= -->
943<div class="doc_subsection">
944 <a name="nano">Microscopic Details</a>
945</div>
946<!-- ======================================================================= -->
947
948<p>This section describes preferred low-level formatting guidelines along with
949reasoning on why we prefer them.</p>
950
951<!-- _______________________________________________________________________ -->
952<div class="doc_subsubsection">
953 <a name="micro_spaceparen">Spaces Before Parentheses</a>
954</div>
955
956<div class="doc_text">
957
958<p>We prefer to put a space before a parentheses only in control flow
959statements, but not in normal function call expressions and function-like
960macros. For example, this is good:</p>
961
962<div class="doc_code">
963<pre>
964 <b>if (</b>x) ...
965 <b>for (</b>i = 0; i != 100; ++i) ...
966 <b>while (</b>llvm_rocks) ...
967
968 <b>somefunc(</b>42);
969 <b><a href="#ll_assert">assert</a>(</b>3 != 4 &amp;&amp; "laws of math are failing me");
970
971 a = <b>foo(</b>42, 92) + <b>bar(</b>x);
972 </pre>
973</div>
974
975<p>... and this is bad:</p>
976
977<div class="doc_code">
978<pre>
979 <b>if(</b>x) ...
980 <b>for(</b>i = 0; i != 100; ++i) ...
981 <b>while(</b>llvm_rocks) ...
982
983 <b>somefunc (</b>42);
984 <b><a href="#ll_assert">assert</a> (</b>3 != 4 &amp;&amp; "laws of math are failing me");
985
986 a = <b>foo (</b>42, 92) + <b>bar (</b>x);
987</pre>
988</div>
989
990<p>The reason for doing this is not completely arbitrary. This style makes
991 control flow operators stand out more, and makes expressions flow better. The
992 function call operator binds very tightly as a postfix operator. Putting
993 a space after a function name (as in the last example) makes it appear that
994 the code might bind the arguments of the left-hand-side of a binary operator
995 with the argument list of a function and the name of the right side. More
996 specifically, it is easy to misread the "a" example as:</p>
997
998<div class="doc_code">
999<pre>
1000 a = foo <b>(</b>(42, 92) + bar<b>)</b> (x);
1001</pre>
1002</div>
1003
1004<p>... when skimming through the code. By avoiding a space in a function, we
1005avoid this misinterpretation.</p>
1006
1007</div>
1008
1009<!-- _______________________________________________________________________ -->
1010<div class="doc_subsubsection">
1011 <a name="micro_preincrement">Prefer Preincrement</a>
1012</div>
1013
1014<div class="doc_text">
1015
1016<p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
1017postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
1018preincrementation whenever possible.</p>
1019
1020<p>The semantics of postincrement include making a copy of the value being
1021incremented, returning it, and then preincrementing the "work value". For
1022primitive types, this isn't a big deal... but for iterators, it can be a huge
1023issue (for example, some iterators contains stack and set objects in them...
1024copying an iterator could invoke the copy ctor's of these as well). In general,
1025get in the habit of always using preincrement, and you won't have a problem.</p>
1026
1027</div>
1028
1029<!-- _______________________________________________________________________ -->
1030<div class="doc_subsubsection">
1031 <a name="micro_namespaceindent">Namespace Indentation</a>
1032</div>
1033
1034<div class="doc_text">
1035
1036<p>
1037In general, we strive to reduce indentation where ever possible. This is useful
1038because we want code to <a href="#scf_codewidth">fit into 80 columns</a> without
1039wrapping horribly, but also because it makes it easier to understand the code.
1040Namespaces are a funny thing: they are often large, and we often desire to put
1041lots of stuff into them (so they can be large). Other times they are tiny,
1042because they just hold an enum or something similar. In order to balance this,
1043we use different approaches for small versus large namespaces.
1044</p>
1045
1046<p>
1047If a namespace definition is small and <em>easily</em> fits on a screen (say,
1048less than 35 lines of code), then you should indent its body. Here's an
1049example:
1050</p>
1051
1052<div class="doc_code">
1053<pre>
1054/// SomeCrazyThing - This namespace contains flags for ...
1055namespace SomeCrazyThing {
1056 enum foo {
1057 /// X - This is the X flag, which is ...
1058 X = 1,
1059
1060 /// Y - This is the Y flag, which is ...
1061 Y = 2,
1062
1063 /// Z - This is the Z flag, which is ...
1064 Z = 4,
1065
1066 /// ALL_FLAGS - This is the union of all flags.
1067 ALL_FLAGS = 7
1068 };
1069}
1070</pre>
1071</div>
1072
1073<p>Since the body is small, indenting adds value because it makes it very clear
1074where the namespace starts and ends, and it is easy to take the whole thing in
1075in one "gulp" when reading the code. If the blob of code in the namespace is
1076larger (as it typically is in a header in the llvm or clang namespaces), do not
1077indent the code, and add a comment indicating what namespace is being closed.
1078For example:</p>
1079
1080<div class="doc_code">
1081<pre>
1082namespace llvm {
1083namespace knowledge {
1084
1085/// Grokable - This class represents things that Smith can have an intimate
1086/// understanding of and contains the data associated with it.
1087class Grokable {
1088...
1089public:
1090 explicit Grokable() { ... }
1091 virtual ~Grokable() = 0;
1092
1093 ...
1094
1095};
1096
1097} // end namespace knowledge
1098} // end namespace llvm
1099</pre>
1100</div>
1101
1102<p>Because the class is large, we don't expect that the reader can easily
1103understand the entire concept in a glance, and the end of the file (where the
1104namespaces end) may be a long ways away from the place they open. As such,
1105indenting the contents of the namespace doesn't add any value, and detracts from
1106the readability of the class. In these cases it is best to <em>not</em> indent
1107the contents of the namespace.</p>
1108
1109</div>
1110
1111<!-- _______________________________________________________________________ -->
1112<div class="doc_subsubsection">
1113 <a name="micro_anonns">Anonymous Namespaces</a>
1114</div>
1115
1116<div class="doc_text">
1117
1118<p>A common topic after talking about namespaces is anonymous namespaces.
1119Anonymous namespaces are a great language feature that tells the C++ compiler
1120that the contents of the namespace are only visible within the current
1121translation unit, allowing more aggressive optimization and eliminating the
1122possibility of symbol name collisions. Anonymous namespaces are to C++ as
1123"static" is to C functions and global variables. While "static" is available
1124in C++, anonymous namespaces are more general: they can make entire classes
1125private to a file.</p>
1126
1127<p>The problem with anonymous namespaces is that they naturally want to
1128encourage indentation of their body, and they reduce locality of reference: if
1129you see a random function definition in a C++ file, it is easy to see if it is
1130marked static, but seeing if it is in an anonymous namespace requires scanning
1131a big chunk of the file.</p>
1132
1133<p>Because of this, we have a simple guideline: make anonymous namespaces as
1134small as possible, and only use them for class declarations. For example, this
1135is good:</p>
1136
1137<div class="doc_code">
1138<pre>
1139<b>namespace {</b>
1140 class StringSort {
1141 ...
1142 public:
1143 StringSort(...)
1144 bool operator&lt;(const char *RHS) const;
1145 };
1146<b>} // end anonymous namespace</b>
1147
1148static void Helper() {
1149 ...
1150}
1151
1152bool StringSort::operator&lt;(const char *RHS) const {
1153 ...
1154}
1155
1156</pre>
1157</div>
1158
1159<p>This is bad:</p>
1160
1161
1162<div class="doc_code">
1163<pre>
1164<b>namespace {</b>
1165class StringSort {
1166...
1167public:
1168 StringSort(...)
1169 bool operator&lt;(const char *RHS) const;
1170};
1171
1172void Helper() {
1173 ...
1174}
1175
1176bool StringSort::operator&lt;(const char *RHS) const {
1177 ...
1178}
1179
1180<b>} // end anonymous namespace</b>
1181
1182</pre>
1183</div>
1184
1185
1186<p>This is bad specifically because if you're looking at "Helper" in the middle
1187of a large C++ file, that you have no immediate way to tell if it is local to
1188the file. When it is marked static explicitly, this is immediately obvious.
1189Also, there is no reason to enclose the definition of "operator&lt;" in the
1190namespace since it was declared there.
1191</p>
1192
1193</div>
1194
1195
1196
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1197<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1198<div class="doc_section">
1199 <a name="seealso">See Also</a>
1200</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1201<!-- *********************************************************************** -->
1202
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1203<div class="doc_text">
1204
1205<p>A lot of these comments and recommendations have been culled for other
1206sources. Two particularly important books for our work are:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1207
1208<ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1209
Chris Lattnerf9f08bf2007-11-09 21:49:08 +0000[diff] [blame]1210<li><a href="http://www.amazon.com/Effective-Specific-Addison-Wesley-Professional-Computing/dp/0321334876">Effective
1211C++</a> by Scott Meyers. Also
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]1212interesting and useful are "More Effective C++" and "Effective STL" by the same
1213author.</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1214
Chris Lattnerf9f08bf2007-11-09 21:49:08 +0000[diff] [blame]1215<li>Large-Scale C++ Software Design by John Lakos</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1216
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1217</ol>
1218
1219<p>If you get some free time, and you haven't read them: do so, you might learn
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]1220something.</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1221
1222</div>
1223
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1224<!-- *********************************************************************** -->
1225
1226<hr>
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]1227<address>
1228 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1232
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]1233 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1234 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1235 Last modified: $Date$
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]1236</address>
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